(i) Field of the Invention
This invention relates to a manual parking mechanism for vehicles with a transmission.
(ii) DESCRIPTION OF THE PRIOR ART
Heretofore, it has been the general practice for a parking mechanism of a vehicle with, for example, a transmission gear system to produce the parking brake force at the time of parking by means of a parking brake device. However, the parking brake is normally used when the engine is off or when parking a vehicle, that is to say, under circumstances where it is difficult to use a booster which is operated by the intake manifold vacuum of the engine or compressed air, so that the braking force has to be applied solely by the hand or foot of a driver although it is relatively weak. In addition, the application of the braking force relies on the tactility of a hand on a brake lever or of a foot on a brake pedal, so that it is not always secure enough. Therefore, as an auxiliary means of the parking brake, the transmission gears are put in a certain gear position at the time of parking a vehicle in engine-off state, thereby engaging the clutch to hold the engine and transmission in directly coupled state and utilizing as parking brake the frictional restraint force of the engine against rotation of the crank shaft. Nevertheless, this frictional restraint force is not strong enough for securely parking a vehicle on steep slopes exceeding a certain gradient.
Therefore, a strong parking brake is required in order to park a vehicle securely. As one method for attaining this, it is known in the art to provide a parking mechanism incorporating into the transmission gear system a parking gear to be used exclusive for the parking purpose, securely locking the output shaft by meshing the parking gear with a lock pole which is fixed on the transmission case. However, the addition of the parking gear and the associated parts invites an increase in cost and makes the parking mechanism complicate.
Illustrated in FIGS. 1 to 3 is a conventional change gear mechanism incorporated into a transmission gear system without a parking mechanism.
Referring to FIG. 1, the transmission gear system which is designated at 100 has first-, second-, third- and fourth-speed drive gears 113 to 116 integrally mounted on an input shaft 112 which is supported in a transmission case 130 by bearings 110 and 111. Rotatably fitted on an output shaft 120, which is supported by bearings 120A and 121A in parallel relation with the input shaft 112, are first-, second-, third-and fourth-speed driven gears 121 to 124 which are constantly meshed with the drive gears 113 to 116, respectively. A couple of adjacent driven gears 121 and 122 are selectively coupled with the output shaft 120 by a first/second speed dog clutch 125 of a known construction including a sleeve 125a, a key 125b, a synchronizer ring 125c, a gear spline 125d and a clutch hub 125e. Similarly, the drive gears 115 and 116 are selectively coupled with the input shaft 112 by a third/fourth speed dog clutch 117 of a known construction including a sleeve 117a, a key 117b, a synchronizer ring 117c, a gear spline 117d and a clutch hub 117e. The transmission gear system is further provided with a driven gear 128 for meshing engagement with a reverse drive gear 118. In this instance, when the first/second speed dog clutch 125 is engaged with the gear 121 by a gear shift mechanism to couple same with the output shaft 120, the rotation of the input shaft 112 is transmitted to the output shaft 120 after a largest speed reduction through gears 113 and 121 to establish the first speed. Similarly, the second speed is obtained by engaging the dog clutch 125 with the driven gear 122, and the third or fourth speed is obtained by engaging the third/fourth speed dog clutch 117 in the grooves of the gear 115 or 116, respectively. The reverse range is established by operation of the reverse gear mechanism 127.
The output shaft 120 has an output gear 129 in meshed engagement with a ring gear 230 of a differential unit 221 in a differential mechanism, thereby transmitting the power of the output shaft 120 from the ring gear 230 to a side gear 234 through a case 231, a pinion shaft 232 and a pinion 233 and then to a drive wheel through an axle 235. Further, as shown in FIGS. 2 and 3: a selector 303; a select and shifter shaft 304 having a shifter cable connecting portion 349 and a select cable connecting portion 342; shift inner lever 305 fixed to the select and shifter shaft 304; and a shifter arm 306 having a groove 361A for a first or second speed shifter arm 361, a groove 362A for a third or fourth speed shifter arm 362 and a groove for a reverse shifter arm 363 respectively engageable with shift inner lever 305, a first or second speed shifter rail 364 mounting thereon a first or second speed shifter fork 365 for operating the first/second speed dog clutch 125 and the first or second speed shifter arm 361, a third or fourth speed shifter rail 366 mounting thereon a third or fourth speed shifter fork 367 for operating the third/fourth speed dog clutch 117 and the third or fourth speed shifter arm 362, and a reverse shifter rail 368 mounting thereon a reverse shifter fork 369 for operating an idler gear (not shown) of a reverse gear mechanism 127 and the reverse shifter arm 363. Especially, in this type of transmission gear system with a fluid type torque converter, a fluid coupling or an electromagnetic clutch, it is necessary to provide a parking mechanism in association with the transmission gear system thereby to couple the engine and the transmission gears in engine-off state for safety purposes, through a select and shifter mechanism. An example of this type of transmission gear system is disclosed in Japanese patent application Laid Open No. 198150/1982, in which is additionally provided a gear mechanism only for parking use.